Bandwidth problems have long restricted the ability of cable television systems to provide private information services to subscribers. Such information services may include Internet access, video-on-demand, games, catalogs, etc. Private services may also include allowing the user to select from among hundreds of less popular programming that is thus made available only on a demand basis. One solution to the limits on system bandwidth has been to assign a portion of cable system bandwidth to conventional or popular channels that are universally broadcast to all subscribers. The remaining available channels are then available for assignment to requesting subscribers on a demand basis.
One such system for providing interactive services on a demand basis is described in U.S. Pat. No. 5,550,578; U.S. patent application Ser. No. 08/551,461 filed Nov. 1, 1995 and U.S. patent Ser. No. 08/987,405 filed Dec. 9, 1997. The full disclosure of each of these patent references is hereby incorporated by reference herein. Basically, the cable service distribution network divides the subscriber pool into various service areas, each served by a different trunk. A first group of channels broadcast to all service areas may provide conventional channels on channels 2 to 73 for example. A second group of channels, 74 to 79, for example, may be reserved for private information services. While the information on channels 2 to 73 is the same in each service area, the information on channels 74 to 79 is different in each service area. Of these channels, those that are in use are individually assigned to a requesting subscriber. A subscriber in one service area may be interacting on channel 74 at the same time a different subscriber in a different service area was also assigned to channel 74. The headend is equipped with the necessary processing, switching or splitting and combining systems for setting up these private channels on demand.
In order to maintain privacy for the private channels, the television signals must be scrambled for distribution and then decoded only at the assigned subscriber's premises. This can result in an increased cost for the cable provider. Conventional scrambling equipment includes an access controller for furnishing signal authorization information such as a decoding key out of band to the user assigned to the scrambled channel. The equipment scrambles a video signal and includes a conditional access code along with the scrambled signal. The conditional access code provider scrambling parameters to the receiving set top so that the signal can be descrambled. The set top will only descramble if it has permission and knows the decoding key for decoding the scrambling parameters. Instead of requiring one complete scrambler for each channel, when broadcasting subscription services, the cable provider implementing the interactive system will need to purchase a scrambler for each interactive channel multiplied by the number of service areas. Increased costs can be a deterrent to implementing an interactive cable system.